In wireless communication systems including transmitters and receivers, antenna array beamforming provides increased signal quality (high directional antenna beamforming gain) and an extended communication range by steering the transmitted signal in a narrow direction. For this reason, such beamforming has been widely adopted in radar, sonar and other communication systems.
The beamforming operation can be implemented either in the analog domain (i.e., before an analog-to-digital (A/D or ADC) converter at the receiver and after a digital-to-analog (D/A or DAC) converter at the transmitter), or in the digital domain (i.e., after the A/D converter at the receiver and before the D/A converter at the transmitter).
In conventional multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) wireless systems, transmit and/or receive beamforming is implemented in the digital domain. Specifically, in such systems, digital beamforming is implemented before an inverse Fast Fourier Transform (IFFT) operation at the transmitter, and after a FFT operation at the receiver.
Though digital beamforming improves performance, such improvement is at the cost of N radio frequency (RF) chains and N IFFT/FFT operations, wherein N is the number of antennas. For digital beamformed MIMO OFDM systems, beamforming vectors are obtained separately for each and every subcarrier, which generally involves a decomposition operation on each subcarrier. Further, singular value decomposition, or eigenvalue decomposition is normally needed. The complexity of such operations further increases as sampling frequency increases.